1. Field of the Invention
The present invention relates to a single-pipe cylinder-type reformer for manufacturing a hydrogen-rich reformed gas by steam-reforming a hydrocarbon-based fuel such as a city gas or LPG and, more particularly, to a reformer used in a solid-state polymer-type fuel cell.
2. Description of the Prior Art
A reformer is an apparatus for generating a reformed gas with a high hydrogen concentration by steam-reforming a raw material gas such as a city gas or LPG, and is widely used when manufacturing hydrogen used in an optical fiber or semiconductor manufacturing process, a fuel cell and the like.
The steam-reforming reaction performed by a reformer is an endothermic reaction, and accordingly heating is needed to sustain the reaction. Usually, a combustor such as a burner is added to the reformer, and excessive hydrogen or reformed raw material gas from a fuel cell is heated by combusting it with the burner. As a reformer for manufacturing a comparatively small volume of hydrogen, for example, a single-pipe cylinder-type reformer as disclosed in Japanese Unexamined Patent Publication No. 11-11901 is known. In this single-pipe cylinder-type reformer, a heating means such as a burner is provided at the center of a cylindrical container comprised of two cylinders with a catalyst layer being stored between them. The catalyst layer is heated by the heating means, and a raw material gas supplied to the catalyst layer is reformed by steam.
The present applicant has previously filed an application for a single-pipe cylinder-type reformer, a fuel cell using the same, and an operating method for the reformer as shown in International Publication No. WO00/63114.
When a solid-state polymer-type fuel cell is to be used in a home or in an automobile, the entire reforming device including the single-pipe cylinder-type reformer must be made compact and lightweight. Also, various types of improvements must be made; e.g. higher-efficiency operation must be realized and the start-up time at the start of operation must be shortened.
For example, the raw material gas must be efficiently pre-heated to reduce the fuel. Overheating of the steam generator must be prevented to make the reformer more convenient to use. The reformer must be held at the necessary temperature and the quantity of heat must be effectively utilized to improve efficiency. External heat dissipation must be suppressed by an effective heat insulating structure. Thermal stress caused by an internal temperature difference must be moderated to realize a high durability. The heat of reaction must be effectively utilized to generate steam efficiently. An operating method that can efficiently cope with a change in operating state is sought.
The reformed gas generated by the conventional single-pipe cylinder-type reformer contains about 10% of CO. When this reformed gas is to be used as the fuel for a solid-state polymer-type fuel cell, the CO concentration must be decreased to about 0.5% by a CO modifier, and CO selective oxidation must be performed by a CO selective oxidizer, so the CO concentration decreases to about 10 ppm. However, providing a CO modifier and a CO selective oxidizer for this purpose independently of the single-pipe cylinder-type reformer is not preferable in terms of downsizing, high efficiency, and start-up performance.
In the single-pipe cylinder-type reformer disclosed in International Publication No. WO00/63114, too much heat is radiated to the outside, and heat is not appropriately supplied to and discharged from the respective portions.